1. Field of the Invention
The present invention relates to an ink supply device for supplying ink to a print head.
2. Description of Related Art
A conventional ink supply device is disclosed in U.S. Pat. No. 4,771,295, for example. The ink supply device is a head integrated-type ink cartridge having an ink tank to which a print head for jetting ink is integrally mounted. A porous member (which will be hereinafter referred to as a "foam" member) impregnated with the ink is provided inside the ink tank. The ink tank is provided with an ink supply passage for communication between the print head and the inside of the ink tank. A filter is disposed at one end (an ink supply opening) of the ink supply passage opening into the ink tank. Further, the ink tank is provided with an atmospheric air communication hole for communication between the inside of the ink tank and atmospheric air. The ink cartridge is mounted on a carriage. The carriage is reciprocated, and simultaneously the print head is driven to jet the ink, thereby printing desired data on printing paper.
Thus, the foam member impregnated with the ink is enclosed in the ink tank. As compared with an ink cartridge that has only the ink enclosed in the ink tank, the above-mentioned ink cartridge with an open-type ink supply mechanism effectively prevents the leakage of the ink from the atmospheric air communication hole owing to the ink retentivity of the foam member. Furthermore, the ink cartridge buffers a pressure fluctuation in the ink tank caused by movement of the ink due to acceleration upon reciprocation of the carriage.
However, the print head and the ink tank are integral with each other in the head integrated-type ink cartridge mentioned above. Accordingly, in replacing the ink cartridge with another one after fully using the ink, the print head is unavoidably thrown away. As a result, a user must bear the cost of a new print head, thus increasing a running cost.
In recent ink jet printers considering such a problem, an ink cartridge having a replaceable ink tank has been used so that only the ink tank can be replaced with another one. FIG. 6 shows such an ink cartridge in schematic section.
As shown in FIG. 6, an ink cartridge 61 includes an ink tank 56 as a resin case and a foam member 52 impregnated with ink. The foam member 52 is enclosed in the ink tank 56. The ink tank 56 is provided with an ink supply opening 60 for supplying the ink to a print head 50 for jetting the ink. A filter 54 is disposed at the ink supply opening 60. The foam member 52 is in close contact with the filter 54. An atmospheric air communication hole 58 is formed through a wall of the ink tank 56 on a side opposed to the filter 54.
The ink cartridge 61 is removably connected to the print head 50 fixed to a carriage (not shown). When the ink in the print head 50 is consumed by printing, suction maintenance, etc., the ink in the foam member 52 is supplied through the filter 54 to the print head 50. When the ink in the foam member 52 is consumed, the atmospheric air is introduced from the atmospheric air communication hole 58 into the foam member 52, thus ensuring full use of the ink and buffering a rapid pressure fluctuation occurring in performing the suction maintenance or the like.
With this structure, the ink cartridge 61 only can be replaced with another one, and the print head 50 can be repeatedly used within its allowable service life. Thus, as compared with the above-mentioned head integrated-type ink cartridge having the print head and the ink tank integral with each other, the running cost can be reduced.
However, to further reduce the running cost of the ink cartridge 61, it is necessary to provide an ink exchanging means at a low cost. Also, it is required that the user can exchange the ink easily without staining his/her hands.
As such ink exchanging means, there has been proposed a method of injecting the ink by using an injector or the like as disclosed in U.S. Pat. No. 4,589,000. In applying this method using the injector to the ink cartridge 61 to supply the ink into the foam member 52, the foam member 52 continues to be used. Accordingly, the foam member 52 deteriorates by the injector in the course of repeatedly supplying ink and is broken into fine fragments. The fine fragments of the foam member 52 are introduced to the filter 54 together with the ink, thus blocking the filter 54 or entering the print head 50 causing deterioration in print quality. Further, there is a possibility of dust entering the foam member 52 upon injection by the injector causing deterioration in print quality.
When the same injector is repeatedly used to supply ink from an ink container storing a large amount of ink to the ink cartridge 61, good quality ink may not be maintained because of a change in concentration of the ink, solidification of the ink, or entry of dust or the like in the injector or the ink container. This problem has conventionally been eliminated by closely storing the ink in the injector and only using the injector once for the supply of the ink to the ink cartridge 61. However, since the injector is thrown away after use continuously replacing the injector increases costs.